ZeroTierOne/node/SharedPtr.hpp

/*
 * Copyright (c)2019 ZeroTier, Inc.
 *
 * Use of this software is governed by the Business Source License included
 * in the LICENSE.TXT file in the project's root directory.
 *
 * Change Date: 2026-01-01
 *
 * On the date above, in accordance with the Business Source License, use
 * of this software will be governed by version 2.0 of the Apache License.
 */
/****/

#ifndef ZT_SHAREDPTR_HPP
#define ZT_SHAREDPTR_HPP

#include "AtomicCounter.hpp"
#include "Mutex.hpp"

namespace ZeroTier {

/**
 * Simple zero-overhead introspective reference counted pointer
 *
 * This is an introspective shared pointer. Classes that need to be reference
 * counted must list this as a 'friend' and must have a private instance of
 * AtomicCounter called __refCount.
 */
template <typename T> class SharedPtr {
  public:
    SharedPtr() : _ptr((T*)0)
    {
    }
    SharedPtr(T* obj) : _ptr(obj)
    {
        ++obj->__refCount;
    }
    SharedPtr(const SharedPtr& sp) : _ptr(sp._getAndInc())
    {
    }

    ~SharedPtr()
    {
        if (_ptr) {
            if (--_ptr->__refCount <= 0) {
                delete _ptr;
            }
        }
    }

    inline SharedPtr& operator=(const SharedPtr& sp)
    {
        if (_ptr != sp._ptr) {
            T* p = sp._getAndInc();
            if (_ptr) {
                if (--_ptr->__refCount <= 0) {
                    delete _ptr;
                }
            }
            _ptr = p;
        }
        return *this;
    }

    /**
     * Set to a naked pointer and increment its reference count
     *
     * This assumes this SharedPtr is NULL and that ptr is not a 'zombie.' No
     * checks are performed.
     *
     * @param ptr Naked pointer to assign
     */
    inline void set(T* ptr)
    {
        zero();
        ++ptr->__refCount;
        _ptr = ptr;
    }

    /**
     * Swap with another pointer 'for free' without ref count overhead
     *
     * @param with Pointer to swap with
     */
    inline void swap(SharedPtr& with)
    {
        T* tmp = _ptr;
        _ptr = with._ptr;
        with._ptr = tmp;
    }

    inline operator bool() const
    {
        return (_ptr != (T*)0);
    }
    inline T& operator*() const
    {
        return *_ptr;
    }
    inline T* operator->() const
    {
        return _ptr;
    }

    /**
     * @return Raw pointer to held object
     */
    inline T* ptr() const
    {
        return _ptr;
    }

    /**
     * Set this pointer to NULL
     */
    inline void zero()
    {
        if (_ptr) {
            if (--_ptr->__refCount <= 0) {
                delete _ptr;
            }
            _ptr = (T*)0;
        }
    }

    /**
     * @return Number of references according to this object's ref count or 0 if NULL
     */
    inline int references()
    {
        if (_ptr) {
            return _ptr->__refCount.load();
        }
        return 0;
    }

    inline bool operator==(const SharedPtr& sp) const
    {
        return (_ptr == sp._ptr);
    }
    inline bool operator!=(const SharedPtr& sp) const
    {
        return (_ptr != sp._ptr);
    }
    inline bool operator>(const SharedPtr& sp) const
    {
        return (_ptr > sp._ptr);
    }
    inline bool operator<(const SharedPtr& sp) const
    {
        return (_ptr < sp._ptr);
    }
    inline bool operator>=(const SharedPtr& sp) const
    {
        return (_ptr >= sp._ptr);
    }
    inline bool operator<=(const SharedPtr& sp) const
    {
        return (_ptr <= sp._ptr);
    }

  private:
    inline T* _getAndInc() const
    {
        if (_ptr) {
            ++_ptr->__refCount;
        }
        return _ptr;
    }
    T* _ptr;
};

}   // namespace ZeroTier

#endif